The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
The present invention relates to a pile driving assembly for installing a pile in an underwater bottom, comprising a tubular pile and a hammer for driving the pile into an underwater bottom.
A known pile driving assembly of the applicant has a tubular pile to be installed in a ground formation and a hydraulic driver including an anvil, wherein the pile has an inwardly protruding circumferential collar at the inside of its upper portion remote from the top side. The known assembly is adapted such that the hammering energy is directly transmitted from the anvil to the pile via the collar. During installation of the pile the hydraulic driver drives the pile into the bottom, for example a seabed. Upon penetrating the bottom the soil material enters the tubular pile. The final position of the pile in the bottom is selected such that the collar inside the pile is below the initial bottom level at the start of driving the pile. This means that in practice in the final position the bottom level in the pile is lower than the bottom level adjacent the pile at the outer side thereof. It is noted that in the final position the pile may project above the bottom in order to prevent soil material from easily entering the pile from above directly after removing the hydraulic driver.
Since the anvil contacts the collar directly the anvil and/or the collar contact the soil material upon approaching the final position of the pile. This means that the soil material inside the pile is compacted during the final period of hammering. Consequently, after removing the anvil the bottom level inside the pile is lower than the bottom level adjacent the pile at the outer side thereof. The compacted soil provides a basis for placing a bearing element in the pile. For example, the pile may be a jacket pile and the bearing element may be a jacket leg of an offshore structure; the jacket leg can be anchored inside the jacket pile by adding grout to the pile.
A disadvantage of the known assembly is that in case of very dense soil material a high resistance arises as soon as the anvil and/or collar contact the soil material inside the pile. In such a case further compacting the soil material in the pile would be unnecessary.